1. Field of the Invention
The present invention relates to a phase shifter used in communication equipment. More particularly, the present invention relates to a phase shifter, which uses Bragg gratings having tunable phase shift functions with respect to input signals in an RF band without using a separate RF device.
2. Description of the Related Art
In general, a phase shifter is used to control a linear phase of an amplifier that is provided at a transmitter/receiver of a mobile communication system, adjust a beam scan angle of a base station antenna, or control a phase of an output signal of a band pass filter for processing an RF signal or a duplexer using a waveguide. In cases of devices for performing a phase modulation with respect to an input signal, such as an amplifier or an antenna of a mobile communication system, a phase of an output signal must be adjusted to a desired level. To this end, the phase shifter having a phase shift function is provided to adjust the phase of the signal to the desired level. In addition, when correcting a phase error of the output signal or synchronizing signals generated from each device of the mobile communication system, the phase shift function is necessary.
The phase shifters for performing the phase shift function are classified into fixed phase shifters for outputting signals by shifting phases of input signals to fixed levels, and tunable phase shifters for shifting the phases of the input signals to desired levels. The fixed phase shifter can be embodied within a simple structure such as that provided by adjusting a length of a transmission line. However, the tunable phase shifter requires a separate phase control circuit including an RF device in order to shift the phase of the input signal to the desired level.
FIG. 1 is a circuit view illustrating a circuit structure of a conventional tunable phase shifter having a phase control circuit. Referring to FIG. 1, a hybrid coupler HC has an input terminal A connected with a signal input terminal PIN, and an output terminal C connected with a signal output terminal POUT, so that a phase of an input signal SIN is shifted at a right angle through a signal path (A-C). Thus, a first signal, which has been phase-shifted at a right angle, is output through the signal path (A-C). In addition, the phase of the input signal SIN is shifted by an angle of 270 degrees through the other signal path (A-B-D-C) of the hybrid coupler HC, so that a second signal, which has been phase-shifted at an angle of 270 degrees, is output through the other signal path (A-B-D-C). Therefore, SOUT, a combined signal of the first and second signals is output through the signal output terminal POUT.
The phase control circuit including varactor diodes VD1 and VD2, which are tunable resonant devices, resistors R1 and R2, and a capacitor C1, is connected between two terminals B and D of the hybrid coupler HC so as to shift the phase of the second signal passing through the other signal path (A-B-D-C) of the hybrid coupler HC. At this time, the phase of the second signal can be shifted by controlling the capacitance of the varactor diodes VD1 and VD2 by adjusting the DC bias voltage Vbias. Thus, a signal having a desired phase can be output through the signal output terminal POUT of the hybrid coupler HC.
FIG. 2 is a sectional view illustrating a mechanical structure of the tunable phase shifter shown in FIG. 1. In FIGS. 1 and 2, the same reference numerals are used to refer to the same elements. In addition, since the operation of the tunable phase shifter shown in FIG. 2 has been already described with reference to FIG. 1, it will not be described in additional detail below. Although the conventional tunable phase shifter having the above structure can obtain the phase-shifted signal through the signal output terminal POUT of the hybrid coupler HC by adjusting the capacitance of the varactor diodes VD1 and VD2, a plurality of components including RF devices must be provided in the conventional tunable phase shifter. Thus, the manufacturing cost for the conventional tunable phase shifter may rise.
Accordingly, a need exists for a system and method for shifting the phase of a signal in the RF band without using separate RF devices.